ii4 Minnesota Plant Diseases. 



saprophytes. A few have, however, learned just the beginnings 

 of parasitism, e. g., those black molds which attack ripe fruits 

 through wounds or thin skins. Since the protoplasm in fruits 

 is in a dormant condition and contains an enormous amount of 

 food material, sugar, etc., the black mold is able to live here, 

 amateur though it may be, as a parasite. Some animal dis- 

 eases have already been mentioned as the result of black mold, 

 though in these cases it is doubtful whether the fungus is actu- 

 ally parasitic, or merely saprophytic. It has in recent years 

 been found that some molds have the power of changing the 

 starchy material into sugars and adepts in this process have 

 been selected and are now used to convert potato starch into 

 sugar; from these sugar solutions, by the action of yeast, alco- 

 hol is then produced. In this process the potato starch is ster- 

 ilized by heat and enclosed in perfectly clean casks, and the fun- 

 gus is then introduced under perfectly clean conditions. When 

 the starch is all converted, the yeast is introduced, also in the 

 pure state, so that the whole process is as carefully conducted 

 as in the culture of bacteria by an expert bacteriologist. By 

 this process the yield of alcohol has been enormously increased. 

 Moreover, some black molds when submerged in a sugar solu- 

 tion have the power of forming alcohol and carbonic acid gas 

 just as do the yeasts ; but they are not vigorous enough to be of 

 economic use. 



Some of the peculiar intoxicating drinks of Asiatic tribes 

 are produced by the introduction of certain black molds and 

 yeasts into starch mixtures. 



Many black molds are also to be found on decaying fungi, 

 as mushrooms, though it is not certain that they are actually 

 parasites, they undoubtedly hasten the decay. (Figs. 14, 16, 

 17, 46.) 



Black-mold parasites (Mucorinea in part}. Closely related 

 to the true black molds are certain forms which live chiefly as 

 parasites on other black molds. They are also found on a few 

 other fungi. If a piece of bread with an abundance of black mold 

 on it be left in moist conditions for some time these parasitic 

 molds almost always appear. They are very minute plants and 

 require high powers of the microscope for their observation. 

 They form a delicate thread mycelium from which fine branches 



